SE,B,389.614 (Ellila) describes a circular flat filter, having an annular filter surface which slopes from the periphery of the filter down towards the centre thereof, wherein liquid to be filtered passes from the periphery of the filter surface to an outlet. Mounted beneath the filter surface is one or more nozzle-equipped pipes which deliver filter-flushing liquid to the filter surface and which rotate together with a flushing-liquid supply pipe located in the centre of the filter. The nozzle orifices of the spray tubes are directed obliquely in relation to the longitudinal extension of respective spray tubes.
SE,B,153.533 (Engstroms Mek. Verkstad) describes a similar flat filter, in which part of the particle-contaminated liquid is flushed away and collected and passed to an outlet via a drainage channel positioned above the filter surface, this channel being defined by a filter cover and the filter surface.
In principle this solution implies that a jet of liquid "brushes" particles away from the filter gauze or filter surface sideways towards an outlet located on one side of the filter gauze (in essence, similar to washing a garage floor with the aid of a water hose). The drawback with this solution is that particles will still block a substantial part of the filter during their movement towards the outlet. This prevents the whole of the filter surface from being used effectively for the purpose intended, namely to extract particles from the particle-contaminated liquid by filtration.
Further examples of the present standpoint of techniques are found in SE,C,194.216 and SE,C,204.133 (both Ellila).
When the liquid delivered to the filter contains large quantities of fibres, the liquid will drain-off very slowly, since the fibres will block the holes in the filter, or screening gauze, even when the fibres are moved towards the centre of the filter by the cleaning jets.